Class 10 Science - Chapter 1: Chemical Reactions and Equations (Detailed
Notes)
1. Introduction
A chemical reaction occurs when one or more substances (reactants) change to form new
substances (products) with different properties.
Example: Magnesium ribbon burns in air to form magnesium oxide.
Mg + O₂ → MgO
2. Chemical Equation
A chemical equation represents a chemical reaction in symbolic form.
Word Equation: Magnesium + Oxygen → Magnesium oxide
Balanced Equation: 2Mg + O₂ → 2MgO
Balancing ensures the number of atoms of each element is equal on both sides (Law of
Conservation of Mass).
3. Types of Chemical Reactions
i) Combination Reaction
Two or more substances combine to form a single product.
Example: CaO + H₂O → Ca(OH)₂ (Exothermic reaction)
ii) Decomposition Reaction
A single compound breaks down into two or more simpler substances.
Thermal: CaCO₃ → CaO + CO₂
Electrolytic: 2H₂O → 2H₂ + O₂
Photolytic: 2AgCl → 2Ag + Cl₂ (in sunlight)
iii) Displacement Reaction
A more reactive element displaces a less reactive element from its compound.
Example: Zn + CuSO₄ → ZnSO₄ + Cu
iv) Double Displacement Reaction
Exchange of ions between two compounds to form new compounds.
Example: Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl
Notes)
1. Introduction
A chemical reaction occurs when one or more substances (reactants) change to form new
substances (products) with different properties.
Example: Magnesium ribbon burns in air to form magnesium oxide.
Mg + O₂ → MgO
2. Chemical Equation
A chemical equation represents a chemical reaction in symbolic form.
Word Equation: Magnesium + Oxygen → Magnesium oxide
Balanced Equation: 2Mg + O₂ → 2MgO
Balancing ensures the number of atoms of each element is equal on both sides (Law of
Conservation of Mass).
3. Types of Chemical Reactions
i) Combination Reaction
Two or more substances combine to form a single product.
Example: CaO + H₂O → Ca(OH)₂ (Exothermic reaction)
ii) Decomposition Reaction
A single compound breaks down into two or more simpler substances.
Thermal: CaCO₃ → CaO + CO₂
Electrolytic: 2H₂O → 2H₂ + O₂
Photolytic: 2AgCl → 2Ag + Cl₂ (in sunlight)
iii) Displacement Reaction
A more reactive element displaces a less reactive element from its compound.
Example: Zn + CuSO₄ → ZnSO₄ + Cu
iv) Double Displacement Reaction
Exchange of ions between two compounds to form new compounds.
Example: Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl
